The maximum energy and/or power densities obtainable from carbon based electrodes in liquid double layer capacitors, batteries, and fuel cells often depend on various physiochemical rate phenomena occurring at the electrode-electrolyte interface. The energy density in liquid double layer capacitors, for example, increases with increased surface area of the carbon electrode material presented to the electrolyte [Tiedemann, W., and Newman, J., J. Electrochem. Soc., 122, 70, (1975)], while the power density is controlled and limited by the diffusion of electrolyte through the microporous electrode material [Rose, F., in "Proceedings of the 33rd International Power Sources Symposium", Cherry Hill, N.J., June 13-16, 1988, The Electrochemical Society, Inc., p. 572 (1988)]. As a result, electrode capacitance depends on an interplay between increased diffusional processes and higher levels of surface area. Since higher levels of surface area entail smaller characteristic dimensions and smaller diffusional pathways, high energy density and high power density are often mutually exclusive.
For Li/SOCl.sub.2 and other battery systems, reaction products tend to clog normal carbon cathodes at higher current densities (&gt;10 mA/cm.sup.2) [Mammone, R. J., and Binder, M., J. Electrochem. Soc., 134, 37, (1987)] as a result of preferential precipitation at the exterior of the electrode. High power density cathode materials are required which are flexible and which have varying and adjustable porosities and void volumes so as to accommodate reaction products without significant loss in accessibility.
In H.sub.2 -O.sub.2 fuel cells and other electrocatalytic processes, the power level and/or reaction selectivity and activity may be restricted by heat and mass transport limitations which occur at the electrode surface [Ticianelli, E. A., Derouin, C. R., Redondo, A., and Srinivason, S., J. Electrochem. Soc., 135, 2209, (1989)]. Porous and flow-through electrocatalysts are desired which incorporate high specific surface areas of supported electrocatalysts such as platinum, palladium, nickel, gold, carbon, etc., while also being present in an easily accessible configuration to facilitate mass transport to active surface regions.
Previous work in this laboratory [Kohler, D. A., Zabasajja, J. N., A. Krishnagopalan, and Tatarchuk, B. J., J. Electrochem. Soc., 137, 136, (1990)] has resulted in a procedure for preparing metal-carbon electrodes which appear to address many of the above mentioned problems associated with double layer capacitors, batteries, and fuel cells. Free standing electrodes, with variable porosities and void volumes, can be manufactured from a wide variety of metal fiber and carbon fiber sources. We now disclose a method of optimizing an electrical property in the preparation of composite electrodes made of high surface area carbon fibers and conductive stainless steel fibers. Stainless steel fibers were chosen because of their commercial availability in small diameters (.ltoreq.4 .mu.m) and their compatibility with a number of electrolytes.